We have an Exchange 2003 environment and had created an exchange 2010 server (hub, mailbox and CAS all in one) Everything works fine receiving and sending mail regardless of which mailbox the user is located on however due to performance issues we need to replace the existing exchange 2010 server with a new one. I created the new server and all the connections to 2003 just as I had done previously and moved a handful of users off the first 2010 server onto the new one. Everything works fine as long as the first exchange 2010 server is on however as soon as I shut down the first EX2010 server, the users who's mailbox is on the second EX2010 server stop receiving external email. They can still send externally and both receive and send internal. Any pointers would be appreciated.